1. Field of the Invention
The present invention relates to an engine automatic-stop/restart system that automatically stops an engine when a predetermined engine automatic stopping condition is satisfied and then restarts the engine when a restarting condition is satisfied.
2. Description of the Related Art
To date, for the purpose of improving the gasoline mileage of a motor vehicle and reducing an environmental load, there has been developed a so-called engine automatic-stop/restart system that automatically cut off the supply of fuel so as to automatically stop an engine, when the operation of a driver (e.g., braking operation while the motor vehicle travels at a speed lower than a predetermined speed) satisfies a predetermined condition for stopping the engine, and then restarts fuel injection so as to automatically restarts the engine, when the operation of the driver (e.g., brake-releasing operation, accelerator stepping-on operation, and the like) satisfies a predetermined condition for restarting the engine.
To date, as such an engine automatic-stop/restart system, there has been proposed a system (for example, refer to Japanese Patent No. 4214401) in which, when an engine restart request occurs after idling-stop driving is performed, speed-governing energization of the starter motor is started; at a time instant when the rotation speed of the starter motor becomes close to an anticipated rotation speed of the engine, the coupling between the pinion gear and the ring gear is started; at a time instant when the rotation speed of the motor (here unit the rotation speed of the pinion gear, and the same applies hereinafter) and the rotation speed of the engine synchronize with each other, the coupling between the pinion gear and the ring gear is ended; after the end of the coupling, full-power energization of the starter motor is performed so that the starter motor drives the engine; then, the restart of the engine is completed.
In the case of the conventional system disclosed in Japanese Patent No. 4214401, before the rotation of the engine completely stops, the engagement between the pinion gear and the ring gear is realized; therefore, it is made possible to restart the engine rapidly.
In addition, to date, there has been proposed a system (for example, refer to Japanese Patent No. 4211208) in which, when an engine restart request occurs after idling-stop driving is performed, it is determined whether or not restart of the fuel supply can restore the engine to a state where it can autonomously rotate; in the case where it is determined that the engine can be restored to the state where it can autonomously rotate, the engine is restarted merely through fuel supply, without the starter being utilized; in the case where it is determined that the engine cannot be restored to the state where it can autonomously rotate, speed-governing energization of the starter motor is performed, firstly, so as to make the motor rotation speed and the engine rotation speed synchronize with each other, and then full-power energization of the starter motor is performed so that the starter motor drives the engine to restart.
In the case of the conventional system disclosed in Japanese Patent No. 4211208, in the case where it is determined that, merely by supplying the fuel, the engine can be restored to the state where it can autonomously rotate, the engine is restarted merely through fuel supply, without the starter being utilized; therefore, the starter is utilized less frequently, whereby the amount of energy consumption can be reduced.
In the case of the conventional system disclosed in Japanese Patent No. 4214401, the engine rotation speed at a time instant when the pinion gear and the ring gear abut on each other is anticipated so that the motor rotation speed is made to synchronize with the engine rotation speed; however, there has been a problem that accurate anticipation of the engine rotation speed burdens an engine control unit (referred to as an ECU, hereinafter), which controls an engine, with a large load.
The conventional system disclosed in Japanese Patent No. 4214401 operates in such a way that, as represented in FIG. 13, when, at a time instant t1 during a time period, immediately after the engine has automatically stopped due to idling-stop driving, in which the engine rotation speed decreases, an engine restart request occurs, speed-governing energization of the starter motor is started; at a time instant t2 when the motor rotation speed becomes close to an anticipated rotation speed of the engine, coupling between the pinion gear and the ring gear is started; at a time instant t3 when the motor rotation speed and the engine rotation speed synchronize with each other, the coupling between the pinion gear and the ring gear is completed; then, at a time instant t4, restarting of the engine is completed. Although the engine rotation speed can be autonomously restored by restarting the fuel supply and it is not required to drive the starter motor, the energization of the starter motor is continued during a time period from the time instant t1 when the engine restart request occurs to the time instant t4 when the restarting of the engine is completed; thus, the starter is utilized more frequently, whereby there has been a problem that energy is wastefully consumed and the starter motor deteriorates faster.
In the case of the conventional system disclosed in Japanese Patent No. 4211208, as represented in FIG. 14A, after the engine has stopped due to idling-stop driving, it is determined, in accordance with the engine rotation speed at a time instant t1 when the engine restart request occurs, whether or not the engine can autonomously be restored to a state where it can rotate, merely by restarting the fuel injection; in the case where it is determined that the engine cannot autonomously be restored to the state where it can rotate, speed-governing energization of the starter motor is started, and then at a time instant t2, the coupling between the ring gear and the pinion gear is started. However, there has been a problem that, when, at a time instant t3 before the coupling is completed, engine combustion causes a rise in the engine rotation speed, noise occurs because the pinion gear and the ring gear strike each other (the state where they cannot synchronize with each other) while the motor rotation speed and the engine rotation speed maintain relative rotation difference, and the noise continues until a time instant t4 when the starting of the engine is completed.
In contrast, in the case of the conventional system disclosed in Japanese Patent No. 4211208, as represented in FIG. 14B, in the case where it is determined, at the time instant t1 when the engine restart request occurs, that the engine cannot autonomously be restored to the state where it can rotate, speed-governing energization of the starter motor is started, and then at the time instant t2, the coupling between the ring gear and the pinion gear is started; however, in the case where, at the time instant t4 after the time instant t3 when the coupling is completed, engine combustion causes a rise in the rotation speed, the time period where synchronization is impossible does not take place; therefore, noise does not occur.
In the case of the conventional system disclosed in Japanese Patent No. 4211208, as represented in FIG. 15, at a time instant t1 when an engine restart request occurs, it is determined that the engine rotation speed cannot autonomously be restored, and at the time instant t1, speed-governing energization of the starter motor is started; however, even though, at a time instant t2 before the coupling of the pinion gear and the ring gear is started, the rotation speed becomes high enough for the engine to be autonomously restored to rotation and hence it is not required anymore to couple the pinion gear with the ring gear, the speed-governing energization of the starter motor continues, and then at a time instant t3, the pinion gear and the ring gear are coupled so that the starter starts the engine; therefore, there has been a problem that energy is wastefully consumed during a time period from the time instant t2 to the time instant t4 and hence the starter deteriorates faster.